Catalytic performance of W/HZSM-5 in selective catalytic reduction of NO by acetylene was investigated in a reaction system with 1600 ppm of NO,800 ppm of C_2H_2,and 9.95% of O_2 in He.It was found that promotional effect of tungsten on the reaction is strongly affected by catalyst preparation conditions and Si/Al ratio of the parent zeolite.A better dispersion of tungsten on HZSM-5 and relatively more monomeric tungsten species were found on 8%W/HZSM-5 prepared by impregnation of the zeolite with lower SiO_2/Al_2O_3 ratio(25)in ammonic ammonium tungstate solution and calcination of the resulting material at higher temperature(550℃).The highest NO conversion to N_2 of 86.3% in the reaction system was obtained at 350℃over the catalyst thus prepared.The mechanism of monomeric tungsten species improving the C_2H_2-SCR can be attributed to accelerating the formation of active nitrate species. Catalytic performance of W / HZSM-5 in selective catalytic reduction of NO by acetylene was investigated in a reaction system with 1600 ppm of NO, 800 ppm of C 2 H 2, and 9.95% of O 2 in He. It was found that the promotional effect of tungsten on the reaction is strongly affected by catalyst preparation conditions and Si / Al ratio of the parent zeolite. A better dispersion of tungsten on HZSM-5 and relatively more monomeric tungsten species were found on 8% W / HZSM-5 prepared by impregnation of the zeolite with lower SiO 2 / Al 2 O 3 ratio (25) in ammonic ammonium tungstate solution and calcination of the resulting material at higher temperature (550 ° C.). highest NO conversion to N_2 of 86.3% in the reaction system was obtained at 350 ° C. over the catalyst prepared. The mechanism of monomeric tungsten species improving the C_2H_2-SCR can be attributed to accelerating the formation of active nitrate species.